john is twice as old as mary. the sum of their ages is 21. how old is mary? let j = john's age and m = mary's age. select the sy stem equations that represents the problem.
1 answer:
Hello, let's assume j the john's age, m the mary's age. <span>"John is twice as old as mary"==>j=2*m </span> <span>"the sum of their ages is 21" ==>j+m=21 ==>2*m+m=21 ==>3m=21 ==>m=7 and j=21-7=14 </span>
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